Balloon for a dilation catheter and method for manufacturing a balloon

ABSTRACT

A method for forming a balloon for a dilation catheter is provided herein. The method includes the steps of: (i) positioning a tube in a preconditioned mold; (ii) expanding the tube in a preconditioned mold to form a parison; (iii) positioning the parison in a balloon mold; and (iv) expanding the parison within the balloon mold to form the balloon. Thus, the tube is initially expanded into a parison in the preconditioned mold. Subsequently, the parison is expanded into a balloon in the balloon mold. Because of this unique manufacturing process, polyester block copolymers can be formed into balloons. Some of these polyester block copolymers could not be formed into a balloon using prior art blow molding processes. The resulting balloon exhibits superior characteristics, including relatively thin and consistent walls, soft texture, low uninflated crossing profile, expansion in a predictable fashion, and good tensile strength.

REFERENCE TO RELATED APPLICATION

[0001] This Application is a Divisional Application of U.S. applicationSer. No. 08/856,419 filed on May 14, 1997. The contents of U.S.application Ser. No. 08/856,419 filed on May 14, 1997 are incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a device for treatinga blockage or stenosis in a vessel of a patient and a method for makingthe device. More specifically, the present invention relates to aballoon for a dilation catheter that is useful for performing medicaldilation procedures such as angioplasty, and/or delivering a stent and amethod for manufacturing the balloon.

BACKGROUND

[0003] It is well known that many medical complications are caused by apartial or total blockage or stenosis of a blood vessel in a patient.Depending on the location of the stenosis, the patient can experiencecardiac arrest, stroke, or necrosis of tissues or organs.

[0004] Several procedures have been developed to treat stenoses,including angioplasty, incising and dilating the vessel, and stenting.These procedures typically utilize a dilation catheter having a balloonto dilate the vessel or deliver the stent. The desired size and physicalcharacteristics of the balloon depend largely upon the size of thevessel and the intended use of the balloon.

[0005] Generally, balloons for dilation catheters are classifiedaccording to their “compliance” or expandability relative to otherballoons. Typically, a balloon is rated as being either “compliant,”“semi-compliant,” or “non-compliant.”A comprehensive definition of theseterms is provided in U.S. Pat. No. 5,556,383, issued to Wang et al. andentitled “Block Copolymer Elastomer Catheter Balloons,” the contents ofwhich are incorporated herein by reference.

[0006] The physical characteristics of the balloon are primarilyinfluenced by how the balloon is formed and by the material utilized inthe balloon. Presently, most balloons are formed from a tube which isheated to above its glass transition temperature and radially expandedin a blow mold. Often, the tube is also subjected to an axial stretch sothat the resulting balloon is biaxially oriented.

[0007] Typically, non-compliant balloons are made from materials, suchas polyethylene terephthalate. These non-compliant balloons are oftenrelatively inflexible, are prone to develop pin holes, and the balloondoes not rewrap well after inflation in the vessel. As a result thereof,these balloons are often difficult to remove from the delivery catheter.Further, if these balloons are used to position a stent in the vessel,the balloon frequently catches on the stent and repositions the stent inthe vessel. On the other extreme, compliant balloons are typically madeof materials, such as polyvinyl chlorides. However, compliant balloonsoften have a relatively low tensile strength, do not expand in apredictable fashion, and are subject to rupture during high pressureapplications.

[0008] Recently, a number of semi-compliant balloons have beenmanufactured using materials, such as nylon and polyamide-polyethercopolymers. These balloons exhibit many desirable characteristicsincluding relatively thin walls, a soft texture, a low uninflatedcrossing profile, thermal stability, and good tensile strength. However,present semi-compliant balloons are not completely satisfactory, sincethese semi-compliant balloons are made by standard blow moldingprocesses. For example, the wall thickness of a balloon manufactured bystandard processes may be inconsistent and/or the balloon may have acompliance curve which is too steep or too flat. This can lead tounpredictable balloon inflation and/or over-inflation of the balloon inthe vessel.

[0009] Further, it has been discovered that certain polymers, whichexhibit desirable physical properties, can not be formed into a balloonusing the present blow molding processes. In fact, these materials,namely certain polyester block copolymers will rupture during a typicalblow molding process. Thus, it is believed that these polyester blockcopolymers have not been used for balloons.

[0010] In light of the above, it is an object of the present inventionto provide a balloon having improved physical characteristics for a widevariety of applications. It is another object of the present inventionto provide a balloon having relatively thin, consistent walls, a softtexture, and a low uninflated crossing profile and a low rewrap profileafter inflation in the vessel. Another object of the present inventionis to provide a balloon which is thermally stable, semi-compliant,expands in a predictable fashion, and has improved tensile strength.Still another object of the present invention is to provide a balloonmade from certain polyester block copolymers. Yet another object of thepresent invention is to provide a simple method for manufacturing aballoon which has greater control over the physical properties of theballoon.

SUMMARY

[0011] The present invention is directed to a balloon for a dilationcatheter and a method for manufacturing a balloon which satisfy theseobjectives. The method for forming the balloon includes the steps ofproviding a tube, positioning the tube in a precondition mold,preconditioning the tube within the precondition mold to form a parison,positioning the parison in a balloon mold, and expanding the parisonwithin the balloon mold to form the balloon.

[0012] As provided in detail below, the unique use of the preconditionmold to form the parison from the tube provides for greater control overthe dimensions and properties of the balloon. Further, certain materialswhich could not be formed into a balloon using prior art blow moldingprocesses can be formed into a balloon using the process provided by thepresent invention.

[0013] As used herein, the term “parison” means and describes thepreform which results from preconditioning the tube in the preconditionmold.

[0014] The step of preconditioning of the tube to form the parisontypically includes radially expanding the tube within the preconditionmold to form the parison. Radial expansion of the tube can beaccomplished by heating the tube to a first temperature (“T1”) andpressurizing a lumen of the tube to a first pressure (“P1”). For thepolyester-block copolymers provided herein, the first pressure P1 is atleast approximately five hundred (500) psi.

[0015] The amount of preconditioning of the tube can vary according tothe material utilized for the tube and the desired physicalcharacteristics of the balloon. For example, the precondition mold canbe sized so that the parison has a parison outer diameter which is atleast over one (1) times larger than a tube outer diameter of the tube.Typically, however, the precondition mold is sized so that the tuberadially expands within the preconditioning mold to form a parisonhaving a parison outer diameter which is between approximately one andone-half (1.5) and two and one-half (2.5) times larger than the tubeouter diameter. More specifically, for some of the embodiments providedherein, the precondition mold is sized so that the parison outerdiameter is approximately one and seven-tenths (1.7) times larger thanthe tube outer diameter.

[0016] Preferably, the step of preconditioning of the tube to form theparison also includes axial stretching of the tube in the preconditionmold. As provided herein, the tube can be axially stretched betweenapproximately one and one-half (1.5) to two and one-half (2.5) anoriginal tube length of the tube. This results in a highly oriented andwork hardened parison which is ready to be formed into the balloon.Further, a wall thickness of the tube is substantially uniformly reducedwithin the precondition mold.

[0017] The balloon mold is typically sized so that parison can beradially expanded in the balloon mold to form a balloon having a balloonouter diameter which is between approximately one and one-half (1.5) andtwo and one-half (2.5) times larger than the parison outer diameter.More specifically, for some of the embodiments provided herein, theballoon mold is sized so that the parison is radially expanded into aballoon having a balloon outer diameter which is approximately two (2)times larger than the parison outer diameter.

[0018] Preferably, the parison is also axially stretched in the balloonmold so that the resulting balloon is highly bi-axially oriented. Asprovided herein, the parison can be axially stretched betweenapproximately one (1.0) to one and one-half (1.5) times the parisonlength of the parison.

[0019] Additionally, it has been discovered that a balloon exhibitingsuperior physical characteristics, including a low crossing profile, alow rewrap profile, a soft texture, thermal stability, andsemi-compliant expansion can be formed from polyester block copolymers.Specifically, it has been discovered that a superior balloon can bemanufactured from a block copolymer which consists of an aromaticpolyester hard segment and an aliphatic polyester soft segment. Forexample, an excellent balloon can be made from the copolymer sold underthe trade name “Peleprene,” by Toyobo, located in Osaka, Japan. Thiscopolymer consists of an aromatic polyester hard segment and analiphatic polyester soft segment. Additionally, it is believed that anexcellent balloon can be made from the copolymer sold under the tradename “Hytrel,” by DuPont, located in Wilmington, Del. This copolymerconsists of a polybutylene terephalate hard segment and a long chain ofpolyether glycol soft segment.

[0020] Importantly, the softening point for the specific polyester blockcopolymers identified above is very close to the melting point of thematerial. For these materials, little strength of the material is lostand little softening occurs during a standard blow mold process. Withthese materials, the pressure needed to initiate expansion of the tubeis very high, typically, at least approximately five hundred (500) psi.With these polyester block copolymers, this would cause the tube torupture prior to forming the balloon using a standard blow moldingprocess. However, these materials can be formed into a balloon utilizingthe unique process provided herein.

[0021] Additionally, the present invention relates to a device formanufacturing a balloon. The device includes a precondition moldsuitable for expanding the tube into a parison and a balloon moldsuitable for expanding the parison into a balloon.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The novel features of this invention, as well as the inventionitself, both as to its structure and its operation, will be bestunderstood from the accompanying drawings, taken in conjunction with theaccompanying description, in which similar reference characters refer tosimilar parts, and in which:

[0023]FIG. 1 is a side plan view of a dilation catheter having featuresof the present invention;

[0024]FIG. 2 is a cross-sectional view of a precondition mold, a parisonand a tube (shown in phantom) having features of the present invention;

[0025]FIG. 3 is a cross-sectional view of a balloon mold, a balloon, anda parison (shown in phantom) having features of the present invention;

[0026]FIG. 4 is a cross-sectional view of a parison having features ofthe present invention;

[0027]FIG. 5 is a cross-sectional view of a balloon having features ofthe present invention;

[0028]FIG. 6 is a graph which outlines one (1) example of therelationship between time, temperature, axial stretch, and pressureduring the expansion of the tube in the precondition mold to form theparison;

[0029]FIG. 7 is a graph which outlines one (1) example of therelationship between time, temperature, axial stretch, and pressureduring the expansion of the parison in the balloon mold to form theballoon; and

[0030]FIG. 8 is a graph which outlines the compliance curve for aballoon made in accordance with the present invention.

DESCRIPTION

[0031] Referring initially to FIG. 1, the present invention is directedto a dilation catheter 10 which utilizes a balloon 12 to treat a vessel(not shown) of a patient (not shown). The balloon 12 provided herein,has improved physical characteristics, including a relatively hightensile strength, a relatively thin wall, a relatively low initialcrossing profile, and a relatively low rewrap profile. Preferredembodiments of the balloon 12 provided herein are semi-compliant, soft,and expand in a predictable manner.

[0032] The improved physical characteristics of the balloon 12 are aresult of the unique process used to manufacture the balloon 12 and thematerial used in forming the balloon 12. However, it is anticipated thatthe unique process can be used with other materials to form compliant ornon-compliant balloons 12.

[0033] As shown in FIG. 1, the dilation catheter 10 includes arelatively thin, flexible length of tubing 14. The balloon 12 ispositioned at the desired location along the length of tubing 14. In theembodiment shown in FIG. 1, the balloon is positioned proximate a distaltip 16 of the dilation catheter 10. The dilation catheter 10 isparticularly useful for dilating a vessel, incising a vessel, and/orpositioning a stent in a vessel of a patient. However, it is believedthat the dilation catheter 10 and balloon 12 may be useful for otherintravascular medical procedures.

[0034] The balloon 12 is manufactured utilizing a unique process whichallows for greater control over the physical characteristics of theballoon 12. Referring to FIGS. 2 and 3, as an overview, the uniqueprocess includes preconditioning a tube 18 (shown in phantom in FIG. 2)in a precondition mold 20 to form a parison 22 and subsequentlyexpanding the parison 22 in a balloon mold 24 to form the balloon 12.Because the tube 18 is preconditioned in the precondition mold 20, thereis greater control over the physical characteristics of the resultingballoon 12 and the balloon 12 can be manufactured from materials whichwould rupture during a normal, prior art, blow molding process.

[0035] For example, it has been discovered that an excellent,semi-compliant balloon 12 can be made from polyester block copolymerssuch as a polyester-polyester block copolymer consisting of an aromaticpolyester as the hard segment and an aliphatic polyester as the softsegment. An example of a suitable block copolymer consisting of anaromatic polyester hard segment and an aliphatic polyester soft segmentis manufactured by Toyobo, under the trade names “PELPRENE S6001,”“PELPRENE S9001.” Additionally, it is believed that other polyesterblock copolymers could be used for the balloon. For example, it isbelieved that the polymer manufactured by DuPont under the trade name“Hytrel” will make an excellent balloon 12.

[0036] Importantly, some polyester block copolymers such as “PELPRENES6001” and “PELPRENE S9001” could not be manufactured using prior artballoon blow molding processes. This is because the pressure required toinitiate expansion of the tube 18 is relatively high, i.e., at or abovefive hundred (500) psi. If a prior art blow molding process was used,the pressure required to initiate expansion would rupture the tube 18prior to the balloon 12 expanding into its final configuration. With theprocess provided herein, the precondition mold 20 prevents radialexpansion of the tube 18 prior to rupture of the tube 18.

[0037] Moreover, the unique manufacturing process provided aboveprovides greater control over the physical characteristics of theballoon 12. Importantly, the dimensions, shape, and physicalcharacteristics of the balloon 12 can be more closely varied andcontrolled utilizing the manufacturing process provided herein.

[0038] Additionally, it is believed that other materials such as PET,nylon, polymers, and other block copolymers can be used for the balloonwith the unique process provided herein. With the use of alternatematerials, it is believed that a compliant balloon 12, a non-compliantballoon 12, or a semi-compliant balloon 12 can manufactured using theprocess provided herein.

[0039] The tube 18 is typically extruded from the material using methodsknown by those skilled in the art. The tube 18 includes a lumen 28, atube inner diameter 30, a tube outer diameter 32, a tube wall thickness34, and a tube length 36 which can be varied according to the desiredsize and strength characteristics of the balloon 12.

[0040] The preconditioning mold 20 preconditions the tube 18 to createthe parison 22. Basically, the precondition mold 20 is used to ready orprecondition the tube 18 for expansion in the balloon mold 24. Therequired design of the precondition mold 20 depends upon the desireddesign of the balloon 12. In the embodiment shown in FIG. 2, theprecondition mold 20 includes a pair of opposed precondition moldopenings 38 and a precondition mold cavity 40 for forming the parison22. The precondition mold openings 38 are each sized and shaped toreceive the tube 18 and are typically right circular cylinder shaped.

[0041] The size and shape of the precondition mold cavity 40 variesaccording to the desired size and shape of the parison 22. In theembodiment shown in FIG. 2, the shape of the precondition mold cavity 40is that of a pair of opposed, truncated right circular cones which areseparated by a right circular cylinder. However, those skilled in theart will recognize that the precondition mold cavity 40 can have analternate shape. For example, the opposed, truncated right circular conecould be replaced with a pair of opposed spherical segments (not shown).

[0042] The precondition mold cavity 40 restricts the expansion of thetube 18 and includes a precondition mold inner diameter (“PMID”) 42 forrestricting the expansion of the tube 18. The size of the preconditionmold cavity 40 depends upon the size of balloon 12 to be manufactured,the material utilized, and the size of the tube 18. For example, in someinstances, it may be beneficial for the PMID 42 to be only slightlylarger, i.e., more than one (1) times larger than the tube outerdiameter 32. Typically, however the precondition mold 20 has a PMID 42which is approximately between one and one-half (1.5) to two and onehalf (2.5) times larger than the tube outer diameter 32. Therefore, fora tube 18 having a tube outer diameter 32 of about 0.035 inches, theprecondition mold 20 has a PMID 42 of between approximately 0.052 inchesand 0.0875 inches. However, it is anticipated that a PMID 42 larger thanapproximately two and one-half (2.5) times the tube outer diameter 32may be useful.

[0043] Preferably, the tube 18 is axially stretched and radiallyexpanded in the precondition mold 20 so that the parison 22 isbi-axially oriented. The amount of axial stretching and radial expansioncan vary according to the requirements of the balloon 12. Referring toFIG. 4, the parison 22 that is formed from the tube 18 in theprecondition mold 20 has a parison outer diameter 44, a parison innerdiameter 46, a parison wall thickness 48, and a parison length 50.

[0044] Typically, the tube 18 is: (i) axially stretched betweenapproximately one and one-half (1.5) to two and one-half (2.5) times theoriginal tube length 36; and (ii) radially expanded so that the parisonouter diameter 44 is between approximately one and one-half (1.5) to twoand one-half (2.5) times larger than the tube outer diameter 32. Theresulting parison 22 is highly oriented and has a parison wall thickness48 which is approximately one-fourth (0.25) the tube wall thickness 34.

[0045] Referring back to FIG. 3, the balloon mold 24 is used to form theballoon 12 from the parison 22. Thus, the design of the balloon mold 24also varies according to the desired design of the balloon 12. In theembodiment shown in FIG. 3, the balloon mold 24 includes a pair ofopposed balloon mold openings 62 and a balloon mold cavity 64. Theballoon mold openings 62 are generally right circular, cylinder shaped.The balloon mold cavity 64 forms the shape of the balloon 12.Accordingly, the balloon mold cavity 64 is shaped similar to the desiredshape of the balloon 12. In the embodiment shown in FIG. 3, the shape ofthe balloon mold cavity 64 is that of a pair of opposed, truncated rightcircular cones which are separated by a right circular cylinder.However, those skilled in the art will recognize that the balloon moldcavity 64 could have an alternate shape.

[0046] The size of the balloon mold cavity 64 depends upon the desiredsize of balloon 12 to be manufactured. Typically, the balloon moldcavity 64 has a balloon mold inner diameter 66 (“BMID”) which isapproximately between one and one-half (1.5) to two and one-half (2.5)times larger than the PMID 42 of the precondition mold 20. For example,for a parison 22 having a parison outer diameter 44 of about 0.065inches, the balloon mold 24 has a BMID 66 of between approximately0.0975 inches and 0.1625 inches. However, it is anticipated that a BMID66 which is less than approximately one and one-half (1.5) times thePMID 42 can be utilized. Similarly, it is also anticipated that a BMID66 which is greater than approximately two and one-half (2.5) times thePMID 42 can be used.

[0047] Typically, the parison 22 is axially stretched and radiallyexpanded in the balloon mold 24 to form the balloon 12. The amount ofaxial stretch and radial expansion depends upon the requirements of theballoon 12. Referring to FIG. 5, the balloon 12 which is formed from theparison 22 in the balloon mold 24 has a balloon outer diameter 70, aballoon inner diameter 72, a balloon wall thickness 74 and a balloonlength 76. Typically, the parison 22 is: (i) axially stretched betweenapproximately one (1) to one and one-half (1.5) times longer than theparison length 50. The resulting balloon 12 is highly oriented and has aballoon wall thickness 74 which is approximately one-third (⅓) theparison wall thickness 48.

[0048] To facilitate radial expansion and axial stretching, theprecondition mold 20 and the balloon mold 24 are preferably heated toheat the tube 18 or the parison 22. This can be accomplished with aheating element (not shown) in the mold 20, 24 or by directing a hotfluid proximate the molds 20, 24. The axial stretching and the radialexpansion typically occur when the material is at or above the glasstransition temperature of the material which is being used.

[0049] Devices and methods for radially expanding and axially stretchinga piece of tubing are well known by those skilled in the art. Forexample, as shown in FIG. 2, a first clamp 56 and a second clamp 58 canbe used to grasp the tube 18 on each side of the precondition mold 20and axially stretching the tube 18. The first clamp 56 also seals one(1) end of the tube 18 by compressing the tube 18. For axiallystretching of the tube 18, the first clamp 56 and/or the second clamp 58can be moved apart by a stepper motor (not shown).

[0050] Again referring to FIG. 2, the tube 18 can be radially expandedby releasing pressurized fluid from a container 60 into the lumen 28 ofthe tube 18. The pressurized fluid can be nitrogen gas, oxygen, or someother suitable fluid which is under pressure.

[0051] Typically, the axial stretching and the radial expansion occursubstantially simultaneously. However, in certain instances, it may bebeneficial for axial stretching to occur before the radial expansion orradial expansion to occur before the axial stretching.

METHOD OF MANUFACTURE

[0052] The following procedure describes how to form what is designed asa three millimeter (3 mm) by twenty millimeter (20 mm) balloon 12 from apolyester-polyester block copolymer sold under the trade name of“Pelprene S6001.” It should be understood that the following procedureis merely provided as an example of a manufacturing process utilizingthe precondition mold 20 and the balloon mold 24.

[0053] The relationship between time, temperature, axial stretch, andpressure, for this particular example, is provided in FIGS. 6 and 7.Importantly, the times, temperatures, pressures, and amount of axialstretching can be varied for a different material, a different size ofballoon 12, or to alter characteristics of the balloon 12.

[0054] Initially, the tube 18 is extruded from the polyester-polyesterblock copolymer to form a tube 18 having a tube inner diameter 30 ofapproximately 0.017 inches, a tube outer diameter 32 of approximately0.035 inches, a tube wall thickness 34 of approximately 0.009 inches,and a tube length 36 of approximately 2.6 centimeters. Subsequently, thetube 18 is placed inside the preconditioning mold 20. For this example,the preconditioning mold 20 has a PMID 42 which is approximately 0.06inches. Referring to FIG. 6, the temperature of the tube 18 is rampedfrom approximately ambient temperature to a first temperature T1, whichis between approximately one hundred and thirty degrees Fahrenheit (130°F.) to one hundred and eighty degrees Fahrenheit (180° F.) andpreferably, approximately one hundred and fifty degrees Fahrenheit (150°F.). The increase in temperature only slightly softens the tube 18 madefrom the polyester-polyester block copolymer. After an initial,approximate fifteen (15) second delay, the tube 18 is radially expandedby applying a first pressure P1 to the lumen 28. The P1 is typicallybetween approximately five hundred (500) to six hundred (600) psi.During this radial expansion, the tube 18 is also axially stretchedapproximately between one and one-half (1.5) to two and one-half (2.5)times the original tube length 36.

[0055] The axial stretch and pressure on the tube 18 in the preconditionmold cavity 40 expands the tube 18 to form the parison 22. Importantly,the size of the precondition mold cavity 40 prevents the tube 18 frombursting during this procedure. Subsequently, the parison 22 is cooleduntil the temperature of the precondition mold 20 is below approximatelyone hundred degrees Fahrenheit (100° F.).

[0056] The result is a highly oriented, work hardened parison 22 havinga parison outer diameter 44 of approximately 0.06 inches and a parisonwall thickness 48 which is approximately one-fourth (0.25) times theoriginal wall thickness.

[0057] Next, the parison 22 is positioned in the balloon mold 24. Inthis example, the balloon mold 24 has a BMID 66 which is approximatelytwo (2) times larger than the PMID 42. In the balloon mold 24, theparison 22 is subjected to a first pressure cycle 78 and a secondpressure cycle 80 to form the balloon 12.

[0058] During the first pressure cycle 78, the parison 22 is quicklyheated from approximately ambient temperature to a second temperature(“T2”), which is between approximately one hundred and eighty degreesFahrenheit (180° F.) to two hundred and ten degrees Fahrenheit (210°F.). After approximately a fifteen (15) second delay, the lumen 28 ispressurized to approximately a second pressure (“P2”) which is betweenapproximately two hundred and seventy (270) to three hundred and ten(310) psi and the parison 22 is axially stretched. After approximatelyseventy-five (75) seconds, the pressure is reduced to approximately onehundred and fifty (150) psi for approximately five (5) seconds.

[0059] Subsequently, in the second pressure cycle 80, the pressure inthe lumen 28 is increased to a third pressure (“P3”) which is betweenapproximately three hundred and fifty (350) to five hundred and fifty(550) psi. The second pressure cycle 80 lasts approximately twenty (20)seconds.

[0060] At this time, the dimensions of the balloon 12 are substantiallyestablished and the balloon 12 is then subjected to the anneal cycle 82.The anneal cycle 82 prepares the balloon 12 for use by internallystabilizing the balloon 12 and relaxing the stress in the balloon 12.The anneal cycle 82 includes raising the temperature of the balloon mold24 to a third temperature (“T3”) which is between approximately onehundred and ninety degrees Fahrenheit (190° F.) to two hundred andtwenty degrees Fahrenheit (220° F.) for forty-five (45) seconds andreducing the internal pressure on the lumen 28 to a fourth pressure(“P4”) which is approximately one hundred and ninety (190) to twohundred and ten (210) psi.

[0061] Finally, the balloon 12 is cooled to ambient temperature. Duringthe cooling of the balloon 12, the internal pressure on the lumen 28 isreduced to between approximately one hundred thirty (130) and onehundred eighty (180) psi and the balloon 12 is cooled until thetemperature of the balloon 12 is below approximately one hundred degreesFahrenheit (100° F.).

[0062] A compliance curve for a balloon 12 made in accordance with theprocedure outlined above is provided in FIG. 8. Importantly, the balloon12 formed by this procedure has improved physical characteristics, suchas being semi-compliant, soft, low crossing profile, and relatively hightensile strength.

[0063] Again, it should be noted that the above steps are merelyexemplary. The temperatures, pressures, and amount of axial stretch canbe varied according to the balloon material utilized and the desiredphysical characteristics of the dilation catheter 10.

[0064] While the particular balloon 12 and method for manufacturing aballoon 12, as herein shown and disclosed in detail, is fully capable ofobtaining the objects and providing the advantages herein before stated,it is to be understood that it is merely illustrative of the presentlypreferred embodiments of the invention and that no limitations areintended to the details of construction or design herein shown otherthan as described in the appended claims.

What is claimed is:
 1. A method for forming a balloon, the methodcomprising the steps of: providing a tube; positioning the tube in aprecondition mold, the precondition mold having a precondition moldinner diameter; preconditioning the tube within the precondition mold toform a parison; positioning the parison in a balloon mold, the balloonmold having a balloon mold inner diameter which is larger than theprecondition mold inner diameter; and expanding the parison within theballoon mold to form the balloon.
 2. The method for forming a balloon ofclaim 1 wherein the step of preconditioning the tube includes the stepof expanding the tube in the precondition mold.
 3. The method forforming a balloon of claim 2 wherein the step of expanding the tubeincludes the steps of heating the tube and pressurizing a lumen of thetube to a first pressure (P1), which is at least approximately fivehundred (500) psi.
 4. The method for forming a balloon of claim 2wherein the step of expanding the tube includes radially expanding thetube so that the parison has a parison outer diameter, which is betweenapproximately one and one-half (1.5) to two and one-half (2.5) timeslarger than a tube outer diameter of the tube.
 5. The method for forminga balloon of claim 4 wherein the step of expanding the tube includesaxially stretching the tube between approximately one and one-half (1.5)to two and one-half (2.5) times a tube length of the tube.
 6. The methodfor forming a balloon of claim 2 wherein the step of expanding the tubeincludes radially expanding the tube so that the parison has a parisonouter diameter which is at least over one (1) times larger than a tubeouter diameter of the tube.
 7. The method for forming a balloon of claim1 wherein the step of expanding the parison includes radially expandingthe parison so that the balloon has a balloon outer diameter which is atleast approximately one and one-half (1.5) times larger than a parisonouter diameter of the parison.
 8. The method for forming a balloon ofclaim 1 wherein the step of preconditioning the tube includes radiallyexpanding the tube so that the parison has a parison outer diameterwhich is between approximately one and one-half (1.5) to two andone-half (2.5) times larger than a tube outer diameter of the tube andthe step of expanding the parison includes radially expanding theparison, so that the balloon has a balloon outer diameter which isbetween approximately one and one-half (1.5) to two and one-half (2.5)times larger than the parison outer diameter.
 9. The method for forminga balloon of claim 1 wherein the step of preconditioning the tubeincludes radially expanding the tube so that the parison has a parisonouter diameter which is at least approximately one and one-half (1.5)times larger than a tube outer diameter of the tube and the step ofexpanding the parison includes radially expanding the parison, so thatthe balloon has a balloon outer diameter which is at least approximatelyone and one-half (1.5) times larger than the parison outer diameter. 10.The method for forming a balloon of claim 1 wherein the step ofproviding a tube includes forming the tube from a polyester blockcopolymer.
 11. The method for forming a balloon of claim 1 wherein thestep of providing a tube includes forming the tube from a blockcopolymer which consists of an aromatic polyester hard segment and analiphatic polyester soft segment.
 12. The method for forming a balloonof claim 1 wherein the step of providing a tube includes forming thetube form a block copolymer which consists of a polybutylene terephalatehard segment and a long chain of polyether glycol soft segment.
 13. Amethod for forming a balloon for a dilation catheter, the methodcomprising the steps of: providing a tube having a tube outer diameterand a lumen; positioning the tube in a precondition mold, theprecondition mold having a precondition mold inner diameter which is atleast approximately one and one-half (1.5) times larger than the tubeouter diameter; heating the tube; forming a parison by pressurizing thelumen at a first pressure (P1) which is at least approximately fivehundred (500) psi, the parison having a parison outer diameter which isat least approximately one and one-half (1.5) times larger than the tubeouter diameter; positioning the parison in a balloon mold, the balloonmold having a balloon mold inner diameter which is at leastapproximately one and one-half (1.5) times larger than the preconditionmold inner diameter; heating the parison in the balloon mold; andforming a balloon from the parison by pressurizing the lumen at a secondpressure (P2).
 14. The method of claim 13 wherein the step of forming aparison from the tube includes axially stretching the tube.
 15. Themethod of claim 13 wherein the step of forming a balloon from theparison includes axially stretching the parison.
 16. The method of claim13 wherein the step of forming a balloon from the parison includes thestep of pressurizing in the lumen to at least approximately threehundred and fifty (350) psi.
 17. The method of claim 13 wherein theballoon is subjected to an anneal cycle in the balloon mold, the annealcycle includes heating the balloon to at least approximately two hundreddegrees Fahrenheit (200° F.) and pressurizing the lumen to at leastapproximately two hundred (200) psi.
 18. A method forming a balloon fora dilation catheter, the method comprising the steps of: providing atube having a tube outer diameter; expanding the tube to form a parison,the parison having a parison outer diameter which is at leastapproximately one and one-half (1.5) times larger than the tube outerdiameter; and expanding the parison to form a balloon, the balloonhaving a balloon outer diameter which is at least approximately one andone-half (1.5) times larger than the parison outer diameter.
 19. Themethod for forming a balloon of claim 18 wherein the step of providing atube includes forming the tube from a polyester block copolymer.
 20. Themethod for forming a balloon of claim 18 wherein the step of providing atube includes forming the tube from a block copolymer which consists ofan aromatic polyester hard segment and an aliphatic polyester softsegment.
 21. The method for forming a balloon of claim 18 wherein thestep of providing a tube includes forming the tube from a blockcopolymer which consists of a polybutylene terephalate hard segment anda long chain of polyether glycol soft segment.